Within the field of chip removing or cutting machining of blanks of metal, development continues with the purpose of making more effective not only the capacity of the tools to carry out the machining in a fast and accurate way, but also the manufacture of the different parts of the tools in the form of basic bodies (holders) and replaceable cutting inserts. A trend in development is to improve the machining results with respect to the precision and surface finish, requiring that the active cutting edge of the cutting insert obtains an exact, predetermined position in relation to the basic body. Another trend is to reduce the costs for the manufacture of the tools. This has, among other things, led to the cutting inserts being made from cemented carbide, which are most commonly occurring on the market, already in connection with the compression-moulding and sintering having obtained a better and better dimensional accuracy. In order to obtain good precision of the cutting inserts, previously it was necessary to subject the same to expensive grinding operations, but with the improved compression-moulding and sintering technique, it has become possible to use direct-pressed, i.e., unground, cutting inserts in more and more applications. Even so, the tool designer still has to take into account a dimensional variation of the order of ±0.5% of the nominal dimensions of the cutting insert. This means that the active edge of the cutting insert very well may end up in the desired position if the outcome of the insert production is good, but when the insert production is not good (so far that the cutting insert has swollen and become longer, or shrunk and become shorter, than intended), the position of the cutting edge in relation to the basic body may deviate to such a high extent from the desired position that the machining precision will be reduced.
Recently, tools have been developed, the interfaces between the basic body and the cutting insert of which are formed with connecting surfaces, which individually include male-like as well as female-like engagement means, and which engage each other. Originally, these connecting surfaces included so-called serration connecting surfaces, of the type that includes a plurality of parallel, male-like ridges and female-like grooves, the ridges of which in one of the connecting surfaces engage the grooves of the other connecting surface, and vice versa. In a next stage of development, the interfaces were refined by the fact that certain ridges were orientated at right or other angles to other ridges, often in combination with the number of ridges being reduced to a minimum. However, common to previously known interfaces, the male-like engagement means are more or less elongate, straight ridges having inclined flanks, which have the purpose of guaranteeing the positioning of the cutting insert as well as the transfer of force from the cutting insert to the basic body, by the fact that the flanks of the ridges should have good contact along the entire length thereof, at the same time as the ridges must not touch the bottom of the appurtenant grooves.
Within the field of chip removing machining, there is a difference between theory and practice. Thus, in theory, it is fairly simple to construct interfaces that have optimal properties in respect of stably fixing the cutting insert and the active cutting edge thereof in an exact predetermined position in relation to the basic body, and guaranteeing a good abutment of all the various forces that act on the cutting insert during operation. However, in practice, the stability and position of the cutting insert are affected by a number of unforeseeable factors, one of the most difficult to master being the varying outcome of the manufacture of the cutting inserts. As long as the outcome gives a good, nominal dimensional accuracy, the intended and calculated surface or line contact, among other things, is obtained between the flanks of the ridges and grooves along the entire length of the flanks, but as soon as even moderate form defects arise, there is a risk that the contact between the flanks is reduced to point contacts or partial line contact. This may in turn result in the cutting insert, initially as well as during operation, being positioned incorrectly in relation to the basic body (by so-called overdetermination), and that the transfer of force between the cutting insert and the basic body becomes inferior.
By European Patent No. 0300172 and U.S. Pat. No. 4,315,706, there are previously known cutting tools having cutting inserts, which are detachably connected to the appurtenant basic bodies via interfaces, which include cross section-wise round male members formed in the connecting surface of the basic bodies, which male members engage female-like engagement means in the underside of the cutting insert. However, in these cases, the female-like engagement means are only partly round seatings or seating surfaces, which are open laterally, and which therefore cannot absorb lateral displacement forces in arbitrary radial directions.
Furthermore, European Patent No. 1405686 discloses a cutting tool in the form of a turning tool, the cutting insert of which is detachably connected to a basic body via a tightening screw as well as via a cylindrical locking pin mounted in the basic body, which locking pin engages a cylindrical hole in the cutting insert, and has the capability of counteracting translation of the cutting insert in relation to the basic body. In practice, however, the screw lacks the capability of rotation-securing the cutting insert in a position in which the active cutting edge of the cutting insert reliably can retain an exact space position in relation to the basic body, since the screw, via the male thread thereof, has a certain play in relation to the female thread of the basic body, and may as well be deflected by the cutting forces. Furthermore, the engagement of the locking pin in the cylindrical hole requires extremely fine tolerances to prevent the cutting insert from moving in relation to the locking pin.